Distillation of coke oven tar



ay 8, 1934. s. P. MILLER ET A1. 1957468 DISTILLATION OF COKE OVEN TAR Filed June 5, 1950 ATTORNEYS atenteci May 8, 1934 TES NT OFFHCE DISTILLATION OF COKE OVEN TAR Application June 3, 1930, Serial No. 459,059

5 Claims.

i This invention relates to a method of melting powdered pitch of high melting point by the sensible heat of freshly formed pitch withdrawn from a still. The resulting mixture of pitches may be blended with tar or pitch to produce pitch products. The invention includes both the method and apparatus for carrying it out.

According to this invention, tar such as coke oven tar, gas house tar, low temperature tar, water gas, tar, etc., is distilled to pitch. The hot, fluid, freshly formed pitch is ydrawn off from the tar still, powdered pitch of high melting point is mixed with it, and the sensible heat of the hot pitch melts the powdered pitch. The sensible heat of freshly formed pitch is customarily dissipated. According to this invention, this sensible heat is used to melt powdered pitch of high melting point which is mixed with it.

Pitch ci high melting point cannot readily be melted by the methods ordinarily employed for melting pitches of lower melting point. Pitches of high melting point do not melt down readily and if, for example, a direct red still is charged with solid pitch and heated, that portion of the pitch adjacent to the part of the still to which the heat is supplied becomes overheated and decomposed. By melting the pitch according to the process of this invention, however, there is no possibility of overheating any portion ci the powdered pitch since no portion of itis heated to a higher temperature than the temperature of the melted pitch in which it is dissolved. The present invention therefore' not only econoinizes in the heat required for melting the pitch by employing the sensible heat of the pitch from the still which would otherwise be lost, but the pitch is melted in such a way that no portion of it is subjected to overheating and the powdered pitch is melted without undergoing any substantial decomposition.

Tar such as coke oven tar may be distilled to pitch, and powdered pitch produced by the distillation of coke oven tar or some other tar such as gas-house tar, etc. may be dissolved in it. The powdered pitch may have the same melting point as the freshly produced pitch in which it is dissolved, or the two pitches may be of quite different melting point. Tar from any suitable source may be distilled to pitch of any melting point and powdered pitch produced from the same or a different tar is dissolved by being added thereto. For example, pitch with a melting point of 300 F., or higher up to, for example, 400 F., or 450 F., resulting from the distillation of coke oven tar may be crushed or ground or powdered (Cl. ISG-76) in any suitable way and this powdered pitch is then added, preferably gradually, to molten pitch of approximately the same melting point resulting from the distillation of coke oven tar.

The melting process is advantageously carried out continuously by continuously drawing off the freshly formed pitch into a reservoir, adding the powdered pitch to the reservoir and stirring it thoroughly into the hot molten pitch while continuously drawing oil the resulting product which is a pitch thoroughly melted and fluid. Tar may be distilled in any suitable type' of still to produce the hot fluid pitch which is drawn olf from the still at a temperature above that necessary to keep it iiuid. The powdered pitch will be added to this melted pitch in a quantity such that the amount of heat required to melt the powdered pitch will be somewhat less than the excess of sensible heat present in the molten pitch over that required to keep the pitch molten. Where it is required to add powdered pitch in excess of this amount, the additional heat necessary to keep the pitch molten may be added to the reservoir in which the powdered pitch and molten pitch are blended, or the additional heat may be supplied to the molten pitch before it enters this reservoir.

The mixed pitch product which results from dissolving powdered pitch in the hot freshly formed pitch may be used in any manner in which fresh hot fluid pitch would be used. According to a preferred method of carrying out the invention, this fluid mixed pitch is blended witha flux resulting from the partial distillation of tar in the proportions required to produce a road tar.

A large tonnage of road tars is produced every year, but the demand is seasonal. During the winter months the demand for road tars is small. During the spring and summer the demand for such tars is large. be used in road tars may be produced during the winter months and may be solidified and then stored until there is a demand for road tars; this solid pitch may then be crushed or ground or otherwise powdered and be added to hot fluid freshly made pitch which may also be pitch of high melting point. The resulting uid mixture of pitches may then'be out back with sufficient flux to produce a desired road tar or pitch. l-ligh melting point pitch which has been allowed to solidify can readily be stored. By storing it during the winter months and then melting it down by the sensible heat of freshly produced pitch. according to the process of this invention, alarge High melting point pitch to source of hot thinly fluid pitch may be made available during those portions of the year according to demand, by a process which melts the pitch with minimum loss and decomposition and at low cost.

It is customary to produce road tars by distilling a mixture oi coke oven tar and gas house tar. The coke oven tar and gas house tar are mixed in such proportions that on distillation a pitch of desired free carbon content and having other specified properties will be produced. In carrying out this invention the distillation of the tar to pitch of high melting point is advantageously so controlled that some decomposition of the tar takes place thereby increasing the free carbon content of the pitch, and road tar can be produced directly by blending high melting point pitch produced from coke oven tar in suitable proportions with a flux also derived from coke oven tar, or with coke oven tar itself. The flux may be a topped tar produced by partial distillation of coke oven tar, or semi-pitch or pitch of low melting point resulting from somewhat further distillation of the tar. The flux may be tar which has not been distilled or tar which has been distilled to any regulated extent such that when blended with high melting point pitch a pitch product of the desired properties will be produced.

The tar may be distilled to pitch of high melting point by steam distillation or vacuum distillation or by distillation in a current of hot gases, preferably in a finely divided state or by distillation in a direct iired still or by distillation in other suitable means. The melting point and free carbon content of the pitch produced depend upon the manner in which it is produced, and where road tars are to be formed the nature 1 of the ilux and the proportions in which the flux and high melting point pitch are blended may be varied depending upon the method of producing the pitch and the source of the tar from which it has been produced in order to produce a blended pitch product of desired melting point and free carbon content, etc.

When tar is distilled by straight distillation in a simple still to pitch with a melting point of 105 F., which is the melting point of one type of road tar, the oil yield will be in the neighborhood of 13-16%. One hundred gallons of tar yields by such a method, for example, of road tar and 15% of distillate. To produce a road tar of high free carbon content by straight distillation methods, it is customary to blend gas house tar with coke oven tar and distill the blended mixture.

Road tars can be produced entirely from coke oven tar by distilling one portion of the coke oven tar to pitch of high melting point and then blending this pitch with a flux produced from another portion of the coke oven tar. Higher oil yields also result; for example, coke oven tar may be distilled to pitch with a melting point of 300 F., or higher. If a pitch of 400 F., is produced, for example, by the distillation of coke oven tar in an ordinary direct fired still, the oil yield is in the neighborhood of 46%. Road tar with a melting point of about 105 F. can be produced by blending about 18-20% of this pitch with ilux of about 60 seconds viscosity Engler (100 cc. at 100 C.). The ilux is produced by distilling 5 to 10% of oils from coke oven tar.

Assuming that 18% of 400 melting point pitch when mixed with 82% of flux gives a road tar of the desired melting point, and, further, that coke oven tar on distillation in a plant still yields 46% of oil and 50% 400 F. melting point pitch with about 4% loss, and that the same tar yields about 6% of distillate and 93% of ilux o 60 seconds viscosity with 1% loss, it will be observed that by blending the high melting point pitch with the iiux 80.5% road tar is produced `from 100 parts of tar with a yield of 17.6% oil allowing 1.9% loss. The oil yield is higher than the yield by straight distillation in a simple still; if road tar is thus produced by blending a flux with a high melting point pitch produced under conditions which tend to give a higher oil yield, still higher oil yields will result. Employing distillation methods which yield 70% or more of distillate on distillation to 400 F. melting point pitch, the oil yield resulting from producing road tar by blending such 400 F. melting point pitch with ilux may be as high as 25% or more.

The amount of powdered pitch which can be added to the freshly produced pitch depends upon the temperature at which this freshly produced pitch leaves the still, upon the melting point of the powdered pitch, and also upon the melting point of the resulting blended pitch prodj:

uct. In general the higher the temperature at which the pitch leaves the still the larger the amount of powdered pitch which can be dissolved in it without cooling it to a point where it will not ilow readily. If the tar is distilled in an ordinary direct iired still with inert gas recirculation through the tar, and pitch with a melting point of 400 F. is produced, this pitch will be drawn off from the still at a temperature in the neighborhood of 450 C. It will still be thinly fluid if cooled to 250 C. for example. As the heat evolved from 400 F. melting point pitch in cooling from 450 C`. to 250 C'. is somewhat greater than the heat required to heat 400 F. melting point pitch from 30 C'. to 250 C., 400 F. melti ing point pitch if drawn ori from the still at 450 C. will melt more than its own volume of powdered 400 F. melting point pitch and produce a fluid mixed pitch with a temperature of 250 C. with a temperature of 450 C. will melt in the neighborhood of 118 parts of powdered pitch of the same melting point to produce a mixed pitch of 250 C. temperature.

Therefore, according to this invention, to

every 6.7 parts by volume of 400 melting point pitch drawn off from the still at 450 C., 7.8 parts of powdered 400 F. melting point pitch may be added to produce a mixed pitch of 400 F. melting point with a temperature of about 250 C. In producing this pitch about 13.4 parts of distillate are obtained. To the mixed pitch at this temperature about 66 parts by weight of flux are added to produce road tar. 4.3 parts of distillate result from distilling tar to thisl 'flux which has a viscosity of 60 seconds. By blending the hot ilux with the 400 F. melting point pitch in suitable mixing apparatus, 80.5 parts of road tar are obtained. The combined distillate amounts to 17.6%; 1.9 parts are lost.

The yields obtained, etc. will Vary depending upon the origin of the tar distilled, the method of distillation, etc.

Fig. 1 is inthe nature of a ilow sheet showing a tar still 1 to which the tar is admitted and from which 400 F. melting point pitch is drawn off into the reservoir 2. Powdered 400 F. melting point pitch from 3 is also delivered to the reservoir 2. An agitator or stirring arm 4 is shown in the reservoir. The pitch is gradually parts of 400 melting point pitch its (iii

withdrawn from the tar still and the powdered pitch is gradually added to the reservoir in predetermined proportions and the powdered pitch is melted in the reservoir by the sensible heat of the pitch from the tar still. A thinly `fluid mixture is produced. This is drawn oh into the blending tank where it is mixed with hot iiuX from 6. An agitator or stirrer 01 suitable design is indicated at 7. The blended pitch produced which is suitable for road tar is drawn off at 8.

By blending the ux and high melting point pitch in different proportions, pitch products suitable for diierent purposes such as for roofing pitch and briquetting pitch, etc. may be produced.

Fig. 2 shows schematically the production of road tar and the yields obtained by the separate distillation of coke oven tar to produce 400 F. melting point pitch and ilux. 7.8 parts or" the 490 F. pitch have been reduced to powder. This is dissolved in 6.7 parts of het freshly formed high melting point pitch and the resulting fluid mixture of high melting point pitch is then blended with parts of ilux. From each 100 parts of coke oven tar treated in this manner 80.5 parts of road tar is produced. The yield of 17.6% distillate is somewhat greater than that obtained by the straight distillation or" a mixture of coke oven tar and gas house tar to produce a road tar of the same melting point. The road tar produced by this process is a very desirable product. t yields but a small percentage of oil on distillation to 355 C. and is therefore a comparatively stable product, losing only a small ercentage oi oil by volatilization after being applied to a road.

In the specication and in the claims by high melting point pitch, we mean a pitch with a melting point such that it can be crushed or ground or otherwise reduced to powder successfully on a commercial scale; for example, pitch with a melting point of 300 F. or 400 F. or higher produced from coke oven tar, gas house tar, carburetted water gas tar, etc.

We claim:

l. rhe method 01 producing pitch products, which comprises distilling tar toV pitch of high melting point, continuously drawing oil the resulting pitch from the still, mixing powdered pitch of high melting point therewith and dissolving the powdered pitch by the sensible heat of the pitch from the tar still, thereby producing a thinly uid mixed pitch, and continuously blending the mixed pitch with a flux to produce a pitch product of the lower melting point.

2. The method of producing a pitch product, which comprises distilling tar to pitch with a melting point of at least 300 F., drawing this pitch ofi from the still, mixing powdered pitch of high melting point therewith and melting the powdered pitch by the sensible heat of the pitch with a melting point of at least 300 F., and blending the resulting mixed pitch with a hot flux.

3. The method of producing road tar, which comprises distilling coke oven tar to pitch of high melting point, drawing thisQ pitch off from the still, dissolving therein a powdered high melting point pitch produced from coke oven tar and blending with this mixed product a coke oven tar iiuX in the proper proportions to produce road tar.

4. The method of preparing molten pitch from a solid comminuted high free-carbon pitch or" the group consisting of comminuted high melting point coal tar pitch and comminuted high melting point water gas tar pitch, which comprises distilling tar to form hot liquid pitch at a temperature above the melting point of the solid pitch, bringing the solid pitch in comminuted form into intimate contact with the hot liquid pitch directly after its formation and while it is yet at a temperature above the melting point of the solid pitch, whereby the solid pitch is melted by the sensible heat of liquid pitch.

5. The method of preparing molten pitch from a solid comminuted high free-carbon pitch of the group consisting of comminuted coal tar pitch having a melting point of at least 356 F. and comminuted water gas tar pitch having a melting point of at least 300 F., which comprises distilling tar to orm hot liquid pitch at a temperature above the melting point of the solid pitch, bringing the solid pitch in comminuted form into intimate contact with the hot liquid pitch directly after its formation and while it is yet at a temperature above the melting point of the solid pitch, whereby the solid pitch is melted by the sensible heat of the liquid pitch.

S. P. MILLER. M. L. HAMLIN. 

